The present invention relates generally to friction joining of metal items together and particularly to a portable device capable of joining an electrical contact button to a fixed electrical conductor while the conductor is conducting massive amounts of current and producing magnetic fields of substantial strength.
Aluminum is made, i.e., reduced from aluminum oxide in a Hall cell by directing large amounts of current through an electrolytic bath containing the aluminum oxide. Large carbon anodes are disposed in the electrolyte and substantial amounts of current are directed into the electrolyte through the anodes. In the process of reducing the aluminum, the carbon of the anode combines with the oxygen of the aluminum oxide such that the anode is consumed in the process. This requires regular periodic replacement of the consumed anodes with new anodes.
The replacement process is facilitated by supporting the anodes on metal bars that are clamped to a large electrical bus that feeds the anodes with the electrical current. On the broad face of the bus are electrical contact buttons that firmly engage and contact the bar when the bar is clamped to the bus.
If contact pressures are not adequate between the anode bar and the button, arcing tends to occur between the bar and the button which increases the electrical resistance between the bar and the button. The increased resistance lowers the flow of current in the cell such that the cell itself becomes less efficient in producing the aluminum. The button, in turn, becomes eroded due to the arcing and must be removed from the bus and a new one welded in place. The large amount of current flow in the bus produces a high strength magnetic field around the bus such that conventional welding techniques are adversely affected, i.e., the bond effected by such techniques is only marginal at best.
When new buses are constructed, the contact buttons can be welded thereon without concern for a potential on and current flow through such buses, as the buses are unconnected and not associated with an operating cell. In order to join new contact buttons to bus bars that are in use in a potline of Hall cells, however, any cell or pot in the line that needs replacement buttons must be disconnected and thereby electrically isolated from the line before personnel can remove the old buttons and weld new ones in their place. The removal of a pot (cell) from a potline is economically costly as the production of the pot is totally interrupted.